The present invention relates to a switch assembly for switching between power sources, such as between utility power and an auxiliary power source such as, for example, a backup power source such as a gasoline or other combustible fuel powered generator. The switch is configured to prevent the occurrence of open-neutral configurations that present the potential for high-voltages, e.g., 240 VAC, to be erroneously applied to 120 VAC equipment or appliances, which may cause damage to the equipment or appliances.
Electrical panels, breaker boxes, or load centers frequently include a main contactor, switch, or breaker, which electrically isolates a series of load breakers from a utility power input. Certain types of load centers, such as transfer switches or transfer panels, are configured to receive another input power source, such as from a generator, to provide electrical power to selected individual loads in the event of a utility power failure. During interruption of utility power, the generator supplies power to the load center, which the load center distributes to the selected or designated circuits of the building. Before activating the generator power supply, the main switch must be disconnected or turned “OFF” to prevent the generator power from back-feeding through the utility conductors. Typically, a user must then manually configure one or more of the switches associated with the load center to electrically connect the desired load circuits to the generator power and electrically isolate the sources associated with the utility and generator power signals.
In order to maintain electrical isolation between the generator power input and the utility power input, the connection/disconnection of the utility power supply and generator power supply must be performed in a specific sequence to ensure electrical isolation of the respective power input sources. Various interlock and switching systems have been developed for carrying out this function. One such system is shown and described in Flegel U.S. Pat. No. 6,621,689 issued Sep. 16, 2003, and the disclosure of which is hereby incorporated by reference in its entirety. While the system shown in the '689 patent controls operation of a main power supply ON/OFF switch and an auxiliary power supply ON/OFF switch, it contains no provisions for controlling operation of neutral switches associated with the main or utility power supply, the auxiliary power supply, and the respective load circuits that are configured to be discretely powered by one of the respective power sources. Still other systems provide discrete switch arrangements wherein operation of individual actuators is associated with the conducting state of the discrete conductor circuits associated with a single conductor.
Proper sequencing of the various conducting states of the neutral and power or “hot” leads associated with the respective loads and alternate power sources is a significant issue when switching both the power (hot) and neutral conductors in power transfer equipment. Failure to break the neutral conductor connection last and make the neutral conductor connection first during the power source switching event results in an open neutral configuration that has the potential to allow high voltages (as much as 240 VAC) to be applied to 120 VAC appliances. It should be readily appreciated that providing voltages that are considerably greater than the voltage for which a particular appliance is rated has various undesirable effects, the least of which is the potential damage to those appliances so subjected. Unfortunately, many prior art devices fail to address such occurrences or require complex switching sequences that could be inadvertently incorrectly performed by users during power source switching activities without proper switch interlock constructions. Unfortunately, providing various switch interlock arrangements tends to complicate the power source switching operation and can increase the cost associated with forming a desired interlocking arrangement.
Therefore, there is a need for a single switch assembly that switches both the hot and neutral wire associated with a given circuit and does so in a manner that both first terminates or breaks the neutral connection associated with the circuit and a first power source and establishes a neutral connection of the circuit with a supplemental or second power source prior to connection of the power conductor with the supplemental power source circuit.
For the above reasons, it is desirable to provide a switch assembly that ensures electrical isolation of the utility power and the generator power during a transfer of the input power from one source to another, and which controls the sequence of operation of neutral and power connection to circuits associated with the utility and generator power supplies. The present invention discloses a switch assembly and method of switching connection of a load to alternate power sources that overcomes one or more of the drawbacks mentioned above. Representatively, the switch assembly includes a single actuator that, when engaged by the user, effectuates the desired sequencing of making and breaking the power and neutral connections between the load circuit and the alternate power sources.
Therefore, a first aspect of the invention contemplates a switch assembly that includes an actuator that is movable between a first position and a second position. The switch assembly includes a first movable element and a second movable element that are operably coupled to one another and the actuator. A positive switch contact arrangement is coupled with the first movable element and a neutral switch contact arrangement is coupled with the second movable element. The positive switch contact arrangement and the neutral switch contact arrangement comprise geometrically different constructions so that moving the actuator between a first position and a second position avoids an open neutral condition.
Another aspect of the invention contemplates a switch assembly having a first neutral contact, a second neutral contact, a first power contact, and a second power contact. The assembly includes a neutral conductor that is movable between a first position in which the neutral conductor is electrically connected to the first neutral contact and is electrically isolated from the second neutral contact and a second position in which the neutral conductor is electrically connected to the second neutral contact and is electrically isolated from the first neutral contact. The power conductor is movable between a first position in which the power conductor is electrically connected to the first power contact and is electrically isolated from the second power contact and a second position in which the power conductor is electrically connected to the second power contact and is electrically isolated from the second power contact. A single actuator effectuates sequential movement of the neutral conductor and the power conductor between their respective first and second positions, such that the neutral conductor remains in its first position after the power conductor moves from its first position, and arrives at its second position before the power conductor arrives at its second position.
Another aspect of the invention that is useable or combinable with one or more of the aspects above contemplates a method of switching a load between a first power source and a second power source. The method includes providing an actuator having a first portion and a second portion. The first portion of the actuator is shaped for cooperation with a neutral conductor that is selectively electrically connectable to one of a first neutral contact and a second neutral contact and is not electrically isolatable from a third neutral contact. The second portion of the actuator is shaped for cooperation with a power conductor that is selectively electrically connectable to one of a first power contact and a second power contact and is not electrically isolatable from a third power contact. The actuator is positionally associated relative to the neutral conductor and the power conductor so that movement of the actuator from a first position to a second position both 1) electrically isolates the neutral conductor from each of the first neutral contact and the second neutral contact before the power conductor is electrically isolated from a respective one of the first power contact and the second power contact and 2) electrically connects the neutral conductor to one of the first neutral contact and the second neutral contact before the power conductor is electrically connected to the other respective one of the first power contact and the second power contact. Such operation prevents open neutral and over power conditions in the underlying circuits and does so in a manner that requires only limited user interaction with the switch assembly to effectuate the desired switching of the load between the first and second power sources.
These and various other features, aspects, and advantages of the invention will be made apparent from the following description taken together with the drawings.